The present invention is directed to paging receivers and particularly to receivers which respond to predetermined paging codes to control on-off operation of the receiver to conserve battery life and to provide other control functions desirable in paging receiver operation.
There exist paging receivers on the market today which are used for selectively paging desired stations in accordance with predetermined tone groupings or paging codes of tone encoded paging signals. Selective paging provides an attractive way of paging stations or personnel without disturbing or distracting other personnel and without requiring the constant monitoring of all paging calls made. In such selective paging systems, carrier waves are usually broadcast from a central transmitter and are modulated with different paging codes or tone groupings as well as speech. The tone groupings in one common arrangement involve a plurality of tones transmitted sequentially in a predetermined order or code. In such paging systems the encoded paging signals are transmitted to a plurality of receivers carried by or located in the vicinity of the personnel to be paged. Each receiver is preset to respond to only one particular tone or paging grouping when such is present or modulated on the carrier wave transmitted from the central transmitter. Specifically, each receiver detects all encoded paging signals transmitted at the central transmitter and applies them to its peculiar or distinct decoder section. If the encoded received paging signal corresponds to the preset paging code for the receiver in question, control signals are caused to be generated. These control signals may be utilized for various purposes such as controlling pulsed operation of the receiver tuning a filter for selecting the various control tones included in the code, producing audible or visual signals, and coupling the received speech to a loudspeaker or other indicator, etc.
In the past problems have arisen in trying to accommodate tones which are closely spaced in frequency. Problems manifest themselves in having the circuitry respond to tones other than the desired tones, which is referred to as "falsing". This would result in the detection of a call which is not desired and result in that particular receiver being unnecessarily engaged. One way of resolving this problem is to utilize high Q circuits to detect the tone frequencies. A characteristic of high Q circuits is that they tend to respond relatively slow to incoming tones. Where a pulser circuit is employed for controlling the operative periods of a receiver, such slow response could result in undesirable operation of the pulser circuit and defeat the purpose of a battery saver since it results in the on/off ratio of battery application being too low for desirable receiver operation.
Accordingly, it is one object of this invention to provide an improved battery saving circuit for paging receivers.
Another object of this invention is to provide an improved circuit for generating control signals to control pulsed operation of the receiver portion and the tuning of a selective filter employed in detecting coded pulse tones.
Another object of this invention is to provide a pulser circuit for use in a pager wherein high Q tone decoding circuits are employed.
Another object of this invention is to provide an improved arrangement for selectively decoding sequential tones to obtain control signals.
Another object of this invention is to provide an arrangement for controlling paging receiver operation and particularly controlling the pulsed battery operation, selective tone tuning and indication thereof.